Prosecutors from the Manhattan and Las Vegas U.S. Attorney’s offices and investigators from the Internal Revenue Service and Drug Enforcement Administration are coordinating their efforts to look into the Las Vegas-based company, people familiar with the matter said.

The criminal probe comes as U.S. authorities step up their scrutiny of casinos’ efforts to prevent money laundering. Regulators have long been concerned about vulnerabilities at casinos, which are complex financial institutions that conduct a large amount of cross-border and cash transactions. Wynn, which is run by casino entrepreneur
Steve Wynn,
is the third major Las Vegas casino company in recent years known to be investigated for possible violations of money-laundering laws.

“We are not aware of any criminal investigation of the company whatsoever and we have serious doubts that any such investigation is taking place,” said
Michael Weaver,
Wynn’s senior vice president of marketing. “No agency has notified the company that it is under any investigation.”

The company hasn’t been accused of wrongdoing.

A letter sent to
Donald Campbell,
Wynn’s outside lawyer, by the IRS criminal investigation division in August requested information on Wynn’s U.S. and foreign clients, its domestic and overseas marketing offices, and its internal controls.

Mr. Campbell didn’t respond to requests seeking comment.

“As a highly regulated business we are in a constant dialogue with regulators and governmental agencies on a variety of matters and the fact that information is requested from us by a governmental agency in no way implies the accusation of any wrongdoing by the company,” Mr. Weaver said. “We do not comment on specific interactions with regulators and agencies, but as a general matter we always fully cooperate with them.”

The letter, which was reviewed by The Wall Street Journal, asked the casino for a list of its biggest customers from 2011 through 2013, along with their dates of birth, Social Security numbers and details from their identification documents. The IRS specified it wants information about the company’s safeguards against money laundering and requested a list of Wynn’s top 100 patrons from North America as well as its top 50 in each of three other regions: Asia, Europe and Latin America, according to the letter.

In the letter, the government also asked for an organizational chart of Wynn senior management and staff working in casino and credit operations. The IRS asked for details of branch offices in the U.S. and abroad that enroll customers into credit programs.

Investigators are trying to determine if Wynn violated the laws through its handling of sports-betting activities and through the casino’s dealings with high-roller gamblers, said some of the people familiar with the matter.

Investigators are also trying to determine whether any of Wynn’s VIP customers laundered the proceeds of drug-trafficking through the company’s casinos, the people said. The investigations are still at early stages, they added.

Since 1985, casinos, like banks, have had to report to regulators large cash transactions by customers. Starting in 2003, casinos also were required to file so-called suspicious-activity reports—long a duty of banks.

The U.S. government has told casinos to improve their compliance standards. Casinos “must continue their progress in thinking more like other financial institutions” to identify money-laundering risks, said
Jennifer Shasky Calvery,
the director of the Treasury Department’s Financial Crimes Enforcement Network, or Fincen, at a conference in June. Fincen, which oversees casinos’ compliance with money-laundering laws, wouldn’t comment beyond those remarks.

In her speech, Ms. Shasky laid out a series of red flags for the industry. She said casinos needed to look at the source of suspicious customer cash and watch out for patrons who: move money into the U.S. through third parties; move cash through casino accounts but don’t gamble much; use cash in casino accounts to buy assets like real estate; leave cash at casinos for long periods and exit casinos with large amounts of chips. Under money laundering laws, Ms. Shasky said, the onus is on casinos to figure out, among other things, how their customers made their money if their activity is suspicious.

Other casino operators have been subject to recent federal government investigations involving money laundering laws, including
Las Vegas Sands Corp.
, the world’s largest casino operator, and
Caesars Entertainment Corp.

In a first-of-its-kind case, Las Vegas Sands agreed in August 2013 to accept the Justice Department’s assertion that the company had failed to report potentially improper financial activity by one of its customers. It paid more than $47 million as part of a non-prosecution agreement that ended the criminal investigation. The figure is roughly the amount prosecutors say Sands gained from the high-roller, who was the largest all-cash gambler the company had to that point, according to the agreement.

A few months later in October 2013, Caesars Entertainment disclosed it was under investigation by the U.S. Treasury and a federal grand jury for possible civil and criminal violations of the Bank Secrecy Act. The company said in public filings that it would fully cooperate with the investigations, which are still active.

Wynn is facing additional government scrutiny. In July, the corruption watchdog in the Chinese territory of Macau said it had launched an investigation into a land deal that paved the way for Wynn’s planned $4.1 billion casino-resort there. The company has said it is cooperating with investigators.

In April 2013, the U.S. Department of Justice disclosed it was conducting a criminal investigation into Wynn’s pledge to donate $135 million to the University of Macau. “We have had no communication from the U.S. DOJ on the matter and we do not believe there is any ongoing investigation,” Mr. Weaver said, adding Wynn had been exonerated by the Securities and Exchange Commission and the Nevada Gaming Control Board in the matter.